Will it be Co-op , Horde “traitors” plus alliance make up a 25 man (or maybe more). Very doubtful that alliance would want to cooperate at all at that point on the xpac. Maybe the “new” horde doesn't need help(or maybe the split has severely crippled the horde).
There are 3 entrances to Org(4 if we come from the air), Maybe one raid made up of alliance (plus their heros) take the front, the “new” horde take the back (with thrall) and meet in the middle? Maybe its an instanced zone where the 2 factions race to take down garrosh.
After the alliance take down garrosh, maybe they feel like sacking org? Horde show up first and deal with garrosh, try to put defense against an entire alliance raid in their capital? Even after dealing with the warchief, maybe this war has left a bad taste in everybody's mouth and both sides feel like settling the war right there and then?
I dont know how well a heroic/normal version would work with alliance/horde joint raid. Probably to much of a pain in the ass for 2 guilds to get together.
2 raids (normal/heroic) in the same shared instance zone could be like wintergrasp/tol barad how they started every couple hours.
But LFR with a built in que wouldn't be too bad for either?
Blizzard knows they can't keep doing the same thing over and over, They might feel like changing things up. This would feel way more epic than a normal patch with another raid for end game.
Sry if this topic/ideas has been brought up a million times.